From: Heiko Carstens <hca@linux.ibm.com>
To: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>,
Janosch Frank <frankja@linux.ibm.com>,
David Hildenbrand <david@redhat.com>,
kvm@vger.kernel.org, linux-s390@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/3] KVM: s390: Increase size of union sca_utility to four bytes
Date: Mon, 25 Nov 2024 14:40:22 +0100 [thread overview]
Message-ID: <20241125134022.14417-E-hca@linux.ibm.com> (raw)
In-Reply-To: <20241125132042.44918953@p-imbrenda>
On Mon, Nov 25, 2024 at 01:20:42PM +0100, Claudio Imbrenda wrote:
> On Mon, 25 Nov 2024 12:50:39 +0100
> Heiko Carstens <hca@linux.ibm.com> wrote:
>
> > kvm_s390_update_topology_change_report() modifies a single bit within
> > sca_utility using cmpxchg(). Given that the size of the sca_utility union
> > is two bytes this generates very inefficient code. Change the size to four
> > bytes, so better code can be generated.
> >
> > Even though the size of sca_utility doesn't reflect architecture anymore
> > this seems to be the easiest and most pragmatic approach to avoid
> > inefficient code.
>
> wouldn't an atomic bit_op be better in that case?
I had that, but decided against it, since the generated code isn't shorter.
And it would require and unsigned long type within the union, or a cast,
which I also both disliked.
next prev parent reply other threads:[~2024-11-25 13:40 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-11-25 11:50 [PATCH 0/3] KVM: s390: Couple of small cmpxchg() optimizations Heiko Carstens
2024-11-25 11:50 ` [PATCH 1/3] KVM: s390: Use try_cmpxchg() instead of cmpxchg() loops Heiko Carstens
2024-11-25 12:18 ` Claudio Imbrenda
2024-11-25 11:50 ` [PATCH 2/3] KVM: s390: Remove one byte cmpxchg() usage Heiko Carstens
2024-11-25 12:16 ` Claudio Imbrenda
2024-11-25 13:37 ` Heiko Carstens
2024-11-25 16:20 ` Claudio Imbrenda
2024-11-25 11:50 ` [PATCH 3/3] KVM: s390: Increase size of union sca_utility to four bytes Heiko Carstens
2024-11-25 12:20 ` Claudio Imbrenda
2024-11-25 13:40 ` Heiko Carstens [this message]
2024-11-25 16:17 ` Claudio Imbrenda
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